A man has died after three men were shot at a wedding reception in south-west Sydney.

The men were at the reception at a function centre on Bareena Street, Canley Vale, when police found them with gunshot wounds about 12.20am (2.20am NZT) on Monday.

A 23-year-old man, Faalau Pisu, was in a critical condition, another man, 27, was in a stable condition and the third man, 25, had a minor injury and was in a stable condition this morning. All three were taken to a nearby hospital.

Mr Pisu has since died.

Police could not confirm media reports he was shot twice in the head.

Investigators have not said what may have led to the shooting.

There were 20 relatives of the men outside Liverpool Hospital, with one man in a Comanchero shirt, 2GB reported.

The seven staff at the hall, which was hired for the reception, tried to calm down attendees and move them to the back of the building, a staff member said.

Some of them were suffering from shock after the shooting outside the function centre, the staff member added.